1. Field of the Invention
The present invention relates to a three-phase separator for separating gas and solids from a three-phase mixture containing liquid, gas and solids, a reactor including such a three-phase separator, and a process for separating gas and solids from a three-phase mixture containing liquid, gas and solids.
2. Description of the Related Art
Three-phase separators for separating gas and solids from a three-phase mixture containing liquid, gas and solids are used in a large number of technical areas, such as in the biological purification of effluent or process water. During the purification of biological effluent or process water, the effluent or process water to be purified is brought into contact with aerobic or anaerobic microorganisms which break down the organic contaminants contained in the effluent predominantly into carbon dioxide and water in the case of aerobic microorganisms, and, in the case of anaerobic microorganisms, predominantly into carbon dioxide and methane. The effluent or process water to be purified is generally supplied continuously to the corresponding reactors in which the biological purification takes place via a feed in the lower reactor region and said effluent or process water is led through a sludge bed located above the feed which, depending on the effluent characteristics and procedure, contains microorganism pellets or microorganism flocs. Here, the reactors must be supplied with the oxygen needed for the growth of the microorganisms during the aerobic purification of effluent or process water, normally in the form of air, the air being at least partially attached to the microorganism agglomerates in the form of gas bubbles during the operation of the reactor. As distinct from this, during the anaerobic purification of effluent or process water, operations are carried out with the exclusion of oxygen; however, during the breakdown of the organic compounds contained in the effluent or process water to be purified, the anaerobic microorganisms form gas in particular containing methane and carbon dioxide, which is also designated biogas, which is partly attached to the microorganism pellets in the form of small bubbles and partly rises upward in the reactor in the form of free small gas bubbles. On account of the attached small gas bubbles, the specific weight of the microorganism pellets or flocs decreases, for which reason at least some of the pellets or flocs rise upward in the reactor. Both in the case of anaerobic and in the case of aerobic purification of effluent or process water, a three-phase mixture containing water, microorganism pellets and gas (bubbles) thus forms in the reactor, from which mixture, in the upper reactor region, gas and solids must be separated in order to be able to discharge purified water from the reactor, for example through one or more overflows.
In order to separate gas and solids from a three-phase mixture containing liquid, gas and solids, a three-phase separator has been proposed in U.S. Pat. No. 5,855,785, which includes a gas hood in the lower region of which one or more plates arranged obliquely are provided in order to cause a liquid flow leading around this plate or these plates, which is intended to ensure good gas/liquid separation at the upper part of the plate(s). During the operation in this three-phase separator, the three-phase mixture containing liquid, gas and solids is led from top to bottom on the at least one plate, as seen from the vertical, the separation of gas from the three-phase mixture taking place at the upper end of the plate(s) and the separation of solids from the mixture being carried out by means of sedimentation of the solids at the lower end of the plate(s) toward the bottom of the reactor, while the purified water rises upward in the reactor.
One disadvantage of this three-phase separator, however, resides in the fact that the separation of solids is carried out downward in the reactor as a result of the microorganism pellets sinking from the lower end of the plate. Therefore, effective solids separation presupposes a sufficiently low flow velocity in the reactor, since otherwise the pellets are entrained upward with the liquid flow. Consequently, the process using the aforementioned three-phase separator is restricted to low liquid flow velocities, for which reason, based on the reactor volume, only a small quantity of water can be purified per unit time and per reactor volume by using said process, and the flexibility with regard to the process management is highly restricted. A further disadvantage of the aforementioned three-phase separator resides in the fact that said separator separates the gas contained in the three-phase mixture and the solids contained therein only inadequately, for which reason the water led away from the reactor has only a comparatively low purity.
WO 96/32177 discloses a three-phase separator which comprises a large number of caps having a V-shaped cross section which are in each case arranged parallel to one another and obliquely upward in relation to the vertical, a horizontally arranged gas hood being provided in the upper region of the caps and extending horizontally through the edges of the caps. During the operation of this apparatus, the three-phase mixture is introduced into the three-phase separator through an inlet region, in order then to be led from bottom to top through the flow channels provided between the individual caps. While the heavy solids contained in the mixture settle during this guidance from bottom to top, lightweight solids and gas contained in the mixture are collected in the gas hood and from there are discharged from the separator.
One disadvantage of the aforementioned separator resides in the fact that the separation of solids and gas contained in the three-phase mixture is primarily carried out in the gas hood and consequently simultaneously. However, the higher the flow velocity through the flow channels provided between the individual caps, the more incomplete is this separation of gas and solids from the mixture since, with increasing flow velocity, some of the solids with the small gas bubbles attached thereto are led past the gas hood and thus remain in the liquid. Consequently, the process using the aforementioned three-phase separator is restricted to low liquid flow velocities, for which reason, based on the reactor volume, only a small quantity of water can be purified per unit time and per reactor volume by using said process, and the flexibility with regard to the process management is highly restricted. Furthermore, with the aforementioned separator, only inadequate separation of gas and solids from the three-phase mixture is achieved.
What is needed in the art is a three-phase separator for separating gas and solids from a three-phase mixture containing liquid, gas and solids which can be operated with a high liquid flow velocity, in order in this way to be able to purify a large quantity of three-phase mixture per unit time and per reactor volume, and which achieves complete or at least virtually complete separation of gas and solids from a three-phase mixture containing liquid, gas and solids, and also a corresponding process for separating gas and solids from a three-phase mixture containing liquid, gas and solids.